x11-servers/xorg-server: Backport security fixes

Backport security fixes for CVE-2017-10971 and CVE-2017-10972 (yes, 2017).
For some reason this was not done when the vulnerabilities were documented
in VuXML, and a typo in the version range in VuXML meant that the entries
never matched.

This fixes a memory disclosure and a couple of buffer overruns.

PR: 220584
Reported by: Vladimir Krstulja
MFH: 2018Q2
Security: ab881a74-c016-4e6d-9f7d-68c8e7cedafb